Oscilloscope Setup and Use
The following is some general background and points on how to acquire signals and take
measurements in ENGR 2031 lab using the Tektronix TDS 2000 series oscilloscopes.
The specific oscilloscope we will use in lab is the TDS 2012B but other oscilloscopes
will be similar in operation. Modern oscilloscopes have more features and abilities than
mentioned here.
Scope Checkout
The purpose of this is to verify the probe calibration and to reset the oscilloscope to the
factory operating settings. You should perform a scope checkout each time you use an
oscilloscope in lab.
To perform a scope checkout:
Make sure the oscilloscope is turned off.
Connect both probes to the calibration input (PROBE COMP, the upper of the two
metal connection points at the bottom right of the screen). This provides a
convenient source of a square wave signal with known amplitude and frequency.
Normally you would also need to connect the scope grounds to an appropriate
ground point, but that is not necessary for a scope checkout.
Turn on the oscilloscope.
Reset the oscilloscope to its factory default settings by pressing the DEFAULT
SETUP button. Some models do not have this button in which case consult the
user manual for how to restore the default settings.
Channel 1 should be turned on (yellow waveform) at this point but channel 2 is not.
Turn on channel 2 by pressing the CH2 MENU button. Channel 2 should now be
on (blue waveform).
Press the AUTOSET button. This is a quick way of selecting settings that may be
appropriate for some measurements. Autoset does not always work well,
depending upon the nature of the signals being measured.
Obtaining Screen Shots of Oscilloscope
First ensure that the Ink Saver is on. This will give a white background for printing. To
set the Ink Saver on, first press the UTILITY button, then select printer Options, and
make sure the Ink saver option is set to on. From the Printer Options under the UTULITY
menu, one can also set the file format (JPEG, etc) and layout (portrait or landscape).
To capture the oscilloscope screen and save it to a flash drive, insert the flash drive and
make sure the oscilloscope recognizes it. Press the SAVE/RECALL button, set the
Action to Save Image, and set the File format to JPEG. You can select the folder to save
to but the default is the root of the flash drive. The first file will be named TEK0000.JPG,
subsequent saves will have the filename increment by 1 each time. Select the Save option
and you should see a picture of a clock show up at bottom right while the file is being
saved.
Operating Settings
As long as you have performed a scope checkout the oscilloscope should start in the
default factory settings. To restore the oscilloscope’s factory default settings, press the
DEFAULT SETUP button.
Under the CH1 and CH2 menus you can verify that probe amplification 1x vs 10x is
consistent with the probe you are using.
Triggering
The triggering settings determine when the oscilloscope starts to acquire data and when it
displays a waveform. Before attempting to acquire a signal, make sure the trigger settings
are appropriate for the signal to be acquired. When properly set, one typically gets a
stable waveform. The trigger settings can be adjusted from the triggering menu accessed
by pressing the TRIG MENU button.
Trigger slope
When using the trigger type Edge, the trigger slope selects whether the triggering point is
on a rising or falling edge when using edge triggering.
Trigger level
When using the trigger type Edge, the level determines what voltage on the slope the
trigger point occurs.
Trigger source
The trigger source specifies what signal will be used as the trigger signal. The trigger
signal can be the signal you are trying to acquire or it can be a different signal. We will
typically use the signal being acquired, i.e. the same channel the signal is being acquired
on.
Trigger Mode
The trigger mode determines when the oscilloscope will start acquiring a signal. When in
Normal mode, the oscilloscope will only acquire and display a signal when a valid trigger
condition occurs. Normal mode allows one to only acquire signals meeting valid trigger
conditions. When in Auto mode, the oscilloscope will acquire and display a signal when a
valid trigger condition occurs or after a certain amount of time. Auto mode allows the
oscilloscope to attempt to acquire a signal even if the trigger condition is not met but it
does not work for isolated and transient signals.
Trigger Coupling
The trigger coupling determines what portions of the signal are passed though. DC
coupling passes all components of the signal. AC coupling blocks the DC component
(anything less than 10Hz).
For what we do in ENGR 2031, we will typically use the following triggering settings
(press the TRIG MENU button to bring up the menu)
Type – Edge
Source – same as channel the signal will be acquired on (CH1 or CH2)
Level – 50% (set by pressing the SET TO 50% button)
Slope – rising
Mode – Auto
Coupling - DC
Acquiring Signals
Acquired signals are converted to digital form and then displayed. The acquisition menu
is brought up by pressing the ACQUIRE button.
Acquisition Mode
The sample acquisition mode samples the signal at evenly spaced intervals. This may not
work well for rapidly varying signals or signals that have narrow pulses. The peak detect
mode typically works better for narrow pulses and rapidly varying signals.
Time Base
The SEC/DIV knob controls the time base for the signal. This controls how often the
signal is sampled and is typically set based on the highest frequency in the signal.
For what we do in ENGR 2031, we will typically use the following acquisition settings
(press the ACQUISITION button to bring up the menu)
Acquisition Mode – Sample
(use the SEC/DIV knob to adjust the time base)
Set the seconds per division to an appropriate setting for the signal you expect to
acquire. For periodic signals typically want to see 1.5 to 2 periods on the screen.
Scaling and Positioning Waveforms
Once a signal is acquired and displayed, it can be adjusted to increase or decrease its size
of move it left/right/up/down on the screen.
Vertical and Horizontal Position
The vertical position of a displayed waveform can be moved using the VERTICAL
POSITION knob. The horizontal position of a displayed waveform can be moved using
the HORIZONTAL POSITION knob.
Volts per Division, Seconds per Division
The displayed waveform can be increased/decreased in size (zoom in or out) using the
VOLTS/DIV and SEC/DIV knobs. The VOLTS/DIV knob changes how many volts each
graticule on the screen corresponds to. There are separate VOLTS/DIV knobs for channel
1 and channel 2. The SEC/DIV knob changes how many seconds each graticule on the
screen corresponds to. There is a single SEC/DIV knob for both channel 1 and channel 2.
Typically you want to zoom in as much as possible while still keeping all the waveform
on the screen necessary for any measurements or analysis.
Measurements
Measurements can be taken using the graticules by measuring the number of divisions
and multiplying but he appropriate values of volts/div or sec/div. This method of taking
measurements is typically only used for estimates as modern oscilloscopes have more
accurate ways of taking measurements.
More accurate measurements using the TDS 2012B can be taken using the cursers or the
automated measurements.
Cursers
To bring up the curser menu, press the CURSER button. From the curser menu you can
choose what signal to take a measurement of, and whether you want a time or amplitude
measurement.
Source – specifies which signal to measure, CH1 or CH2
Type of Curser – amplitude or time
Amplitude gives two horizontal cursers that can be moved to get a vertical measurement
in Volts (oscilloscope determines difference between the two cursers in Volts). The
cursers can be moved with the multipurpose knob. The active curser (the one that can be
moved) is selected by selecting either Curser 1 or Curser 2 in the Curser menu. Time
gives two vertical cursers that can be moved to get a horizontal measurement in seconds
(oscilloscope determines difference between the two cursers in seconds). The cursers can
be moved with the multipurpose knob.
Automated Measurements
To bring up the automated measurements menu, press the MEASURE button. The
oscilloscope does all the calculations for automatic measurements, but not all
oscilloscopes have this feature.
The TDS 2012B lets you set take several automatic measurements at the same time. Ones
that you will find useful for ENGR 2031 are:
Freq – gives the frequency of the waveform
Period – gives the period of the waveform
Rise Time – gives the time between 10% and 90% of the first rising edge of the
waveform
Fall Time - gives the time between 90% and 10% of the first falling edge of the
waveform
Min – gives the minimum value of the waveform
Max – gives the maximum value of the waveform
Pk – Pk – gives the peak to peak voltage
For what we do in ENGR 2031, we will typically take measurements using the cursers
and then verify the result using the automated measurements.
Other Useful Items
AUTOSET
Pressing this button causes the oscilloscope to attempt to obtain a stable waveform. The
vertical scale, horizontal scale, and triggering settings are all automatically adjusted by
the oscilloscope. This is in many cases is often the easiest way to acquire and display a
signal but it may not always work.
SINGLE SEQ
Pressing this button causes the oscilloscope to acquire a single waveform and then stop.
This is useful for capturing one-time events.
RUN/STOP
Pressing this button causes the oscilloscope to either: continuously acquire and display a
waveform or stop the acquisition and hold the displayed waveform on the screen.
Stopping the acquisition and holding the waveform is useful when would otherwise keep
acquiring identical sweeps. Measurements or saving/printing can then be done on the
displayed waveform. RUN/STOP should not be used to try and catch an isolated event by
trial and error.
General Procedure for Acquiring Stable Waveforms
Make sure the probe attenuation is set to match the Probe menu selection in the
oscilloscope. Tthe 10x setting allows for full use of the oscilloscope's bandwidth.
To acquire a signal using an oscilloscope (AUTOSET can do most of this but does not
always work)
Connect probe(s) to desired point of circuit
Set up the triggering
Set time base (horizontal scale)
Set vertical scale (volts/div)
Use RUN/STOP or SINGLE SEQ to capture one waveform
Once signal is displayed, adjust the positioning as needed
Take any appropriate measurements and save waveform